The present invention relates to a catalyst, which is improved in terms of ease of preparation, activity and lifetime, for the selective reduction with ammonia of nitrogen oxides contained in oxygen-containing exhaust gases, e.g. stackgases from power plants, based on an intimate mixture of the active constituents
(A) titanium and PA1 (B) tungsten as well as vanadium, iron, niobium and/or molybdenum PA1 (A) titanium as constituent (A), PA1 (B.sub.1) tungsten as the first constituent B, and PA1 (B.sub.2) at least one of the metals vanadium, iron, niobium, and/or molybdenum as the second constituent (B),
each in the form of oxides of the said metals, with an atomic ratio of constituent (A) to (B) of 1 : 0.001 to 1, preferably 1 : 0.003 to 0.3.
Catalysts with these basic materials and similar atomic ratios constitute the subject of German Patent No. 2,458,888. With these known catalysts it is essential that the constituents (A) and (B) be obtained as an intimate mixture in the form of their oxides. According to this prior patent, this object is achieved by using titanium oxide in the form of one of its chemical precursors, such as titanium hydroxide, a titanium salt or titanic acid. This precursor is then combined with soluble or precipitated compounds of the metals of the constituent (B), and is then further processed by pyrolysis to produce the desired oxide material.
It has now been found that equivalent or superior catalyst formulations of the basically known type are more easily accessible if the constituent (A) is used in the form of an oxide obtained from titanium tetrachloride by using flame hydrolysis.